A British Airways flight was struck by what is believed to be a drone as it came in to land at Heathrow Airport, police said.
The pilot of flight BA727 from Geneva in Switzerland reported being hit as the Airbus A320 bound for Terminal Five approached the London hub on Sunday afternoon with 132 passengers and five crew on board.
It is the latest and most serious in a string of incidents involving drones at the airport, with several near misses between flights and un-manned aircraft reported in the last year.
And it raises the issue of regulation and control of drones, especially in sensitive areas like airports.
BA said aircraft was examined by engineers and cleared to take off for its next flight following the incident.
Steve Landells, flight safety specialist at the British Airline Pilots Association (Balpa), said: "Frankly it was only a matter of time before we had a drone strike given the huge numbers being flown around by amateurs who don't understand the risks and the rules.
"It appears that no serious damage was done on this occasion, but what is clear is that while most drones are flown safely, sensibly and within the limits of the law, much more education of drone users and enforcement of the rules is needed to ensure our skies remain safe from this threat."
The Civil Aviation Authority (CAA) "drone code" says the unmanned craft should not be flown above 400 feet and kept away from planes, helicopters, airports and airfield. Those with cameras fitted should also be kept 50m from people, vehicles, buildings and other structures.
A report last month by the UK Airprox Board (UKAB) found there were 23 near misses between drones and aircraft in the six months between April and October last year, including two at Heathrow.
On September 22 a Boeing 777 that had just taken off reported that a drone narrowly passed down its right hand side. Investigators concluded that the drone was at the same height and within 25 metres of the jet. A report was made to police but the drone operator was not traced.
Days later, on September 30, a drone was flown within a few metres of an Airbus A319 landing at Heathrow. The pilot told the UKAB the drone may have been just 20 feet (six metres) above and 25 yards (23 metres) to the left when it passed by the aircraft.
The jet was flying at an altitude of 500 feet and was on the final approach to the west London airport when the drone was spotted.
The Government is also considering technology to restrict where civilian drones can fly amid growing concerns. Transport Minister Robert Goodwill said that ministers are looking at the possibility of introducing a drone registration scheme in the UK, similar to the ones already in place in Ireland and the US.
The Department for Transport has confirmed it is also talking to manufacturers about introducing so-called geo-fencing technology in their drones.
A CAA spokesman said: "Anyone operating a drone must do so responsibly and observe all relevant rules and regulations.
"The rules for flying drones are designed to keep all airspace users safe. It is totally unacceptable to fly drones close to airports and anyone flouting the rules can face severe penalties including imprisonment."
A Scotland Yard spokeswoman said a pilot on an inbound flight into Heathrow Airport from Geneva "reported to police that he believed a drone had struck the aircraft" at around 12.50pm.
She said: "The flight landed at Heathrow Terminal Five safely. It transpired that an object, believed to be a drone, had struck the front of the aircraft."
No one has been arrested and aviation police based at Heathrow are investigating, she added.
A BA spokesman said: "Our aircraft landed safely, was fully examined by our engineers and it was cleared to operate its next flight."